DETECTION OF SUBMONOLAYER O-18 ON A GOLD SURFACE BY NUCLEAR-REACTION ANALYSIS

A gold substrate is the preferred solid surface for formation of an or ganic self-assembled monolayer (SAM). Device fabrication process may r equire the gold film to be exposed to photolithographic processing and plasma treatment prior to molecular assembly. It has been observed th at oxygen plasma treatment prevents the formation of SAMs: however, su bsequent treatment with an argon plasma allows assembly of the organic monolayers. To understand the mechanisms involved, a plasma containin g 98% O-18 was used and the film surface was analysed using the O-18(p , alpha)N-15 nuclear reaction. A proton beam energy of 830 keV was cho sen because a broad resonance in the excitation curve maximises the ox ygen detection sensitivity. A silicon surface barrier detector was emp loyed to detect alpha particles. The analysis showed that after oxygen plasma treatment the gold layer was covered with about 0.8 x 10(15) o xygen atoms cm-2. The presence of this oxygen submonolayer prevents th e sulfur-gold chemical interaction taking place as an essential precur sor to the organic monolayer formation.